Department of Radiation Oncology, University of California San Francisco, San Francisco, California.
Department of Radiation Oncology, University of California San Francisco, San Francisco, California.
Pract Radiat Oncol. 2017 Nov-Dec;7(6):e559-e567. doi: 10.1016/j.prro.2017.04.001. Epub 2017 Apr 9.
To evaluate the influence of a new commercial transmission detector on radiation therapy beams.
A transmission detector designed for online treatment monitoring was characterized on a TrueBeam STx linear accelerator with 6-MV, 6-flattening filter free, 10-MV, and 10-flattening filter free beams. Measurements of percentage depth doses, in-plane and cross-plane off-axis profiles at different depths, transmission factors, and skin dose were acquired with 3 × 3, 5 × 5, 10 × 10, 20 × 20, and 40 × 40 cm field sizes at 100 cm and 80 cm source-to-surface distance (SSD). A CC04 chamber was used for all profile and transmission factor measurements. Skin dose was assessed at 100, 90, and 80 cm SSD using a variety of detectors (Roos and Markus parallel-plate chambers and optically stimulated luminescent dosimeters [OSLDs]). Skin dose was also assessed for various patient sample plans with OSLDs.
The percentage depth doses showed small differences between the unperturbed and perturbed beams for 100 cm SSD (≤4 mm depth of maximum dose difference, <1.2% average profile difference) for all field sizes. At 80 cm SSD, the differences were larger (≤8 mm depth of maximum dose difference, <3% average profile difference). The differences were larger for the flattened beams and larger field sizes. The off-axis profiles showed similar trends. Field penumbras looked similar with and without the transmission detector. Comparisons in the profile central 80% showed a maximum average (maximum) profile difference between all field sizes of 1.0% (2.6%) and 1.4% (6.3%) for 100 and 80 cm SSD, respectively. The average measured skin dose increase at 100 cm (80 cm) SSD for a 10 × 10 cm field size was <4% (<35%) for all energies. For a 40 × 40 cm field size, this increased to <31% (≤63%). For the sample patient plans, the average skin dose difference was 0.53% (range, -6.6% to 10.4%).
The transmission detector has minimal effect on clinically relevant radiation therapy beams for intensity modulated radiation therapy and volumetric arc therapy (field sizes 10 × 10 cm and less). For larger field sizes, some perturbations are observable that would need to be assessed for clinical impact.
评估一种新的商业传输探测器对放射治疗束的影响。
本研究设计了一种用于在线治疗监测的传输探测器，在 TrueBeam STx 线性加速器上对 6-MV、6 型平帽滤波器自由、10-MV 和 10 型平帽滤波器自由射线进行了特性评估。在 100 cm 和 80 cm 源皮距（SSD）处，使用 3×3、5×5、10×10、20×20 和 40×40 cm 射野大小，分别测量了不同深度的百分深度剂量、平面内和平面外离轴轮廓、透射因子和皮肤剂量。使用 CC04 室进行了所有的轮廓和透射因子测量。使用 Roos 和 Markus 平行板室和光激励发光剂量计（OSLD）等各种探测器，在 100、90 和 80 cm SSD 处评估了皮肤剂量。还使用 OSLD 对各种患者样本计划进行了皮肤剂量评估。
在所有射野大小下，对于 100 cm SSD（最大剂量差深度≤4mm，平均轮廓差<1.2%），未受干扰和受干扰光束的百分深度剂量差异较小。在 80 cm SSD 处，差异较大（最大剂量差深度≤8mm，平均轮廓差<3%）。差异在平帽射线和较大射野中较大。离轴轮廓显示出相似的趋势。有和没有传输探测器时，射野半影看起来相似。在所有射野大小中，在轮廓中心 80%处进行比较时，100 和 80 cm SSD 的最大平均（最大）轮廓差异分别为 1.0%（2.6%）和 1.4%（6.3%）。对于 10×10 cm 的射野大小，所有能量在 100 cm（80 cm）SSD 处的平均测量皮肤剂量增加均<4%（<35%）。对于 40×40 cm 的射野大小，增加至<31%（≤63%）。对于样本患者计划，平均皮肤剂量差异为 0.53%（范围，-6.6%至 10.4%）。
对于强度调制放射治疗和容积弧形治疗（射野大小为 10×10 cm 及以下），传输探测器对临床相关放射治疗束的影响很小。对于较大的射野，观察到一些需要评估临床影响的干扰。
